A motor grader has a main frame, a draft frame coupled to the main frame for movement relative to the main frame, a circle gear mounted to the draft frame to rotate relative thereto about a central axis of the circle gear, a moldboard coupled to the circle gear to rotate with the circle gear, and a circle drive configured to rotate the circle gear relative to the draft frame.
A type of circle drive has a single-worm circle drive gearbox with a single worm that meshes with a worm gear operatively coupled to a pinion gear meshing with the circle gear, the worm and the worm gear providing a worm gear set of the circle drive. A single hydraulic motor of the circle drive is operatively coupled to the worm to apply torque to and rotate the worm gear set so as to rotate the circle gear and the moldboard coupled thereto selectively in opposite first and second directions about the central axis of the circle gear.
The worm gear set has a reduced useful life due to durability issues. The worm and the worm gear are made of dissimilar materials so that they do not weld themselves together during operation. The worm gear is made of a softer material than the worm so as to be the sacrificial part (e.g., worm gear made of high-strength manganese bronze and worm made of hardened steel). The sliding action between the worm and the worm gear causes wear on the worm gear, wear being a function of worm rotational speed and applied torque. As such, the worm gear eventually wears to the point of fracture, leading to downtime for replacement of the worm gear.